It depends on a few things, mainly the altitude.
Being strapped onto an aircraft flying at low altitudes may look frightening, but is fully surviveable. In fact, “wing-walking” where people sit outside an aircraft in flight is quite a popular stunt by adventurers, such as this skydiver sitting casually on the wing of a glider in flight.
But this is of course a well rehearsed stunt and performed on fairly low altitude and at low speed.
Myself having jumped out of airplanes while skydiving from about 12.000 feet, I can assure you that the air is cold and the speed of the wind against any unprotected skin makes it a ton worse.
At airliner cruising altitudes (33.000 feet), the ambient air temperature is about minus 50–60˚C, or minus 70˚F. That is the freezing temperature of petrol.
Unprotected skin will develop frost bite in less than one minute and a human body without sufficient thermal protection will develop severe and fatal hypothermia in less than half an hour. And that is if you are protected from the wind by for instance hiding in the unpressurized wheel wells.
If fully exposed to the violent rush of cold air, such as sitting on top of the aircraft cruising at 500 knots, the gruesome chilling effect will happen much sooner, freezing off limbs and tearing off frozen tissue already after a few minutes.
Needless to say, holding on to something, like an antenna, is impossible. Your muscles simply do not have the strength to hold on. It is like hanging freely from a ledge in a blizzard - a few minutes tops, if you are fit and strong and pumping with adrenaline.
But even if you managed to survive this somehow, hypoxia will make you pass out already after a couple of minutes. The air is very thin at cruising altitudes - actually just a fourth of the density at sea level. Even though the oxygen percentage is still the same (21%), there are simply less air molecules for you to breathe in. Hence, the brain will quickly start to shut down.
It will not feel like suffocating and you will not experience anything particularly unpleasant except a shortness of breath, dizziness, fatigue and an irresistible urge to close your eyes to sleep. Events will appear distant and unrelated to you and you will stop caring. Even if you try your best to stay awake, you will pass out in just a few minutes.
Quite contrary to what many people believe, humans are remarkably tolerent to hypobaric hypoxia (caused by high altitudes) and it will not cause immediate brain damage or death. The brain shuts down all non-essential functions to work with the low amount of oxygen to stay alive. However, circulation to the limbs will stop, acceleraring the frostbite effect on fingers, toes, nose and ears. The brain sacrifices these for itself to stay alive. Significant brain damage or death doesn’t occur before as much as 20–40 hours.